The Role of Isostasy in the Evolution of Thin-Skinned Fold and Thrust Belt

2021 ◽  
Author(s):  
Youseph Ibrahim ◽  
Patrice Rey
Keyword(s):  
Numerical Experiments ◽  
Basal Layer ◽  
Structural Evolution ◽  
Geological Model ◽  
Thrust Belt ◽  
Isostatic Adjustment ◽  
Flexural Response ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Fold And Thrust Belts

<p>The stacking of thrust sheets and mass transfer of sediment during fold and thrust belt accretion imposes a load on the basement and underlying mantle. This load induces an isostatic adjustment through a flexural response, which may also contribute to the overall architecture of the fold and thrust belt. Whereas plate kinematics imposes its tempo to evolving fold and thrust belts, the rheology of the mantle controls the tempo of the isostatic flexure. Using two-dimensional high-resolution numerical experiments, we explore how the interplay between the tectonic compressional rate and the isostatic flexural rate influences the structural evolution and final architecture of fold and thrust belts. </p><p>We run a suite of numerical experiments using the well-tested code Underworld. Our geological model is mapped over a 42 km by 16 km numerical grid, with a cell resolution of 80 m. The geological model consists from top to bottom of  ‘sticky air’, 4 km of sediment that alternates in competence at 500 m intervals, a 3 km thick basement, and a basal layer which - in combination with a basal kinematic boundary condition - controls the amount of isostatic flexure. Materials have a mechanical behavior that results from elasto-visco-plastic rheology. The pressure at the base of the model is held constant, and the vertical velocity is updated at each timestep. The amount of material entering or exiting the model at each point along the base scales with the density of the basal layer, which is used to control the isostatic rate. Sedimentation and erosion are self-consistent through mechanical erosion and a hillslope diffusion law. Our models show that as the ratio between tectonic and flexural rates decreases (i.e. flexure gets faster), fold and thrust belts become narrower, lower in elevation, and structurally more complex. We compare these results with natural analogs including the Cordilleran and Jura fold and thrust belts.</p>

scholarly journals Control of 3D tectonic inheritance on fold-and-thrust belts: insights from 3D numerical models and application to the Helvetic nappe system

2019 ◽  
Author(s):  
Richard Spitz ◽  
Arthur Bauville ◽  
Jean-Luc Epard ◽  
Boris J. P. Kaus ◽  
Anton A. Popov ◽  
...  
Keyword(s):  
3D Model ◽  
Swiss Alps ◽  
Thrust Belt ◽  
First Order ◽  
Tectonic Inheritance ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Model Configuration ◽  
Fold And Thrust Belts ◽  
Half Graben

Abstract. Fold-and-thrust belts and associated tectonic nappes are common in orogenic regions. They exhibit a wide variety of geometries and often a considerable along-strike variation. However, the mechanics of fold-and-thrust belt formation and the control of the initial geological configuration on this formation are still incompletely understood. Here, we apply three-dimensional (3D) thermo-mechanical numerical simulations of the shortening of the upper crustal region of a passive margin to investigate the control of 3D laterally variable inherited structures on the fold-and-thrust belt evolution and associated nappe formation. We consider tectonic inheritance by applying an initial model configuration with horst and graben structures having laterally variable geometry and with sedimentary layers having different mechanical strength. We use a visco-plastic rheology with temperature dependent flow laws and a Drucker-Prager yield criterion. The models show the folding, detachment and horizontal displacement of sedimentary units, which resemble structures of fold and thrust nappes. The models further show the stacking of nappes. The detachment of nappe-like structures is controlled by the initial basement and sedimentary layer geometry. Significant horizontal transport is facilitated by weak sedimentary units below these nappes. The initial half-graben geometry has a strong impact on the basement and sediment deformation. Generally, deeper half-grabens generate thicker nappes and stronger deformation of the neighboring horst while shallower half-grabens generate thinner nappes and less deformation in the horst. Horizontally continuous strong sediment layers, which are not restricted to inital graben structures, cause detachment folding and not overthrusting. The amplitude of the detachment folds is controlled by the underlying graben geometry. A mechanically weaker basement favors the formation of fold nappes while stronger basement favors thrust sheets. The applied model configuration is motivated by the application of the 3D model to the Helvetic nappe system of the French-Swiss Alps. Our model is able to reproduce several first-order structural features of this nappe system, namely (i) closure of a half-graben and associated formation of the Morcles and Doldenhorn nappes, (ii) the overthrusting of a nappe resembling the Wildhorn and Glarus nappes and (iii) the formation of a nappe pile resembling the Helvetic nappes resting above the Infrahelvetic complex. Furthermore, the finite strain pattern, temperature distribution and timing of the 3D model is in broad agreement with data from the Helvetic nappe system. Our model, hence, provides a first-order 3D reconstruction of the tectonic evolution of the Helvetic nappe system based on thermo-mechanical deformation processes.

From Fold-and-Thrust Belts on Salt to Salt Deposition and Tectonics in a Fold-and-Thrust Belt, Sivas, Turkey

2015 ◽  
Author(s):  
Jean-Claude Ringenbach* ◽  
Etienne Legeay ◽  
Charlie Kergaravat ◽  
Jean-Paul Callot
Keyword(s):  
Thrust Belt ◽  
Salt Deposition ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Fold And Thrust Belts

Spatio-temporal structural evolution of the Kohat fold and thrust belt of Pakistan

2021 ◽  
Vol 145 ◽  
pp. 104310
Author(s):  
Humaad Ghani ◽  
Edward R. Sobel ◽  
Gerold Zeilinger ◽  
Johannes Glodny ◽  
Irum Irum ◽  
...  
Keyword(s):  
Structural Evolution ◽  
Thrust Belt ◽  
Fold And Thrust Belt ◽  
Spatio Temporal

Structure of the Gare Kakheti foothills using seismic reflection profiles: implications for kinematic evolution of the Georgian part of Kura foreland fold-and-thrust belt

2020 ◽  
Author(s):  
Alexander Razmadze
Keyword(s):  
Cross Sections ◽  
Seismic Reflection ◽  
Structural Evolution ◽  
Foreland Basin ◽  
Thrust Belt ◽  
Fault Propagation ◽  
Seismic Reflection Data ◽  
Growth Strata ◽  
Kinematic Evolution ◽  
Fold And Thrust Belt

<p>Gare Kakheti foothills are located between Lesser Caucasus and Kakheti Ridge and are mainly represented by the series of NEN dipping thrust faults, most of which are associated with fault‐related folds. Gare Kakheti foothills as a part of the Kura foreland fold-and-thrust belt developed formerly as a foreland basin (Oligocene-Lower Miocene) (e.g. Alania et al., 2017). Neogene shallow marine and continental sediments in the Gare Kakheti foothills keep the record on the stratigraphy and structural evolution of the study area during the compressive deformation. Interpreted seismic profiles and structural cross-sections across the Udabno, Tsitsmatiani, and Berebisseri synclines show that they are thrust-top basins. Seismic reflection data reveal the presence of growth fault-propagation folds and some structural wedges (or duplex). The evolution of the Udabno, Tsitsmatiani, and Berebisseri basins is compared with simple models of thrust-top basins whose development is controlled by the kinematics of competing for growth anticlines. Growth anticlines are mainly represented by fault-propagation folds. The geometry of growth strata in associated footwall synclines and the sedimentary infill of thrust-top basins provide information on the thrusting activity in terms of location, geometry, and age.<br>This work was supported by Shota Rustaveli National Science Foundation (SRNSF - #PHDF-19-268).</p><p> </p>

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